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Conventional amputation prosthetics are problematic because they rely on the stump-socket interface for attachment. Intraosseous transcutaneous amputation prostheses (ITAP) could solve these problems; however they rely on the integrity of the soft tissue-implant interface as a barrier to exogenous agents, and in the prevention of downgrowth and marsupilisation. We have used an in vivo animal model to study the soft tissue interfaces around bone-anchored transcutaneous implants. We hypothesise that by facilitating and increasing the area of dermal attachment to the implant epithelial down-growth will be reduced. A flange with a series of 24, 0.7 mm holes positioned immediately below the epithelium was used to increase dermal attachment. This significantly reduced downgrowth and optimised the integrity of the collagenous tissue-implant interface at the dermal level. We postulate that the flange reduces relative interfacial movement at the epithelium-implant interface by providing increased surface area for dermal tissue attachment. A tight seal at the dermal tissue level reduces the degree of downgrowth around ITAP, eliminating marsupilisation as a potential failure modality. Surface topography and coatings did not affect the degree of downgrowth or dermal attachment to straight or flanged implants. A significant negative correlation was observed between downgrowth and both epithelial and dermal attachment. This study shows that a soft tissue-implant interface capable of preventing downgrowth and marsupilisation can develop around a bone-anchored transcutaneous implant, given the incorporation of a porous flange positioned in the dermal tissues immediately below the epithelium. This will benefit applications where bone-anchored transcutaneous implants are used.

The main problem facing the longevity of total joint replacements is wear particle-induced osteolysis, particularly around the acetabular component. Ovine Total Hip Replacement surgery was performed with roughened femoral heads in order to enhance wear debris generation in vivo. The resistance to aseptic loosening of acetabular components with different surface coatings was investigated. Implants remained in vivo for 1 year.Sheep were randomly assigned to one of six experimental groups where the acetabular cup was fixed utilising an: (a) cemented polyethylene acetabular cup, (b) metal backed grit blasted surface, (c) metal backed plasma sprayed titanium porous coating, (d) metal backed sintered beaded coating, (e) Hydroxyapatite (HA)-coated grit blasted surface (f) and HA-coated porous components. Ground Reaction Force (GRF) was used to asses the functional performance of the implants and data was collected pre-operatively and at 12, 24, 36 and 52 weeks post op. Wear debris generated was analysed and radiographs taken prior to preparation of thin sections. Fibrous tissue (FT) thickness and bone contact at 1 mm intervals along the acetabular bone-implant interface was calculated.GRF data demonstrated significant differences between experimental groups. In all groups there was an increase in the function of the hip after surgery and up to 24 weeks but thereafter the function of the group with the grit blasted surface reduced whereas the function of the other groups did not significantly change. Average wear particles generated were < 1 mum in size. The cemented group demonstrated a significantly thicker average FT layer (2.69 mm) when compared with all other groups (p < 0.05 in all cases) except the grit blasted group (1.56 mm). HA porous coated cups demonstrated significantly least fibrous tissue adjacent to its interface when compared with all other groups (cemented p < 0.05, grit blasted p = 0.029, porous p < 0.05, sintered beads p < 0.05 and HA grit blasted p < 0.05). Significantly increased bone contact to HA-coated porous cups (73.33%) when compared with all groups was identified except HA-coated grit blasted cups where no significant difference was demonstrated. Radiographic signs of loosening were visible in all groups except the HA-coated porous group.Results demonstrated that HA porous coated acetabular components significantly enhanced bone ingrowth in the presence of wear particles, preventing their migration and reducing osteolysis. Non-HA-coated porous and sintered beaded components provided a more effective seal against the ingress of wear debris when compared with cemented cups. (C) 2004 Elsevier Ltd. All rights reserved.

The success of clinical results obtained with many hydroxyapatite (HA)-coated prosthetic designs has deflected attention from the need to extend the life of the HA coating on the device. In the current study the percentages of HA and titanium surfaces to which bone was bonded, on HA-coated and non-coated titanium femoral stems retrieved from human subjects, were evaluated. Plasma-sprayed hydroxyapatite (PSHA)-coated devices demonstrated wide variability in the percentage of the PSHA coating remaining on the stems. The coating was missing from a substantial portion of a stem after only about 6 months of implantation. The percentage of revealed metal to which bone was bonded was significantly less than the percentage of the HA coating demonstrating such bonding. The revealed metal to which bone was bonded was comparable to the same value for a separate group of non-PSHA-coated titanium stems. If HA-coatings degrade over time precipitous decline in performance may occur even after several functional years. Many ultrastructural features of the bone bonded to the HA coatings on these implants from human subjects were comparable to those found on HA-coated devices implanted in a canine model.

The use of glass ionomer as a bone graft expander was investigated in an in vivo model of revision hip arthroplasty. Bone grafts of pure allograft and allograft + glass ionomer particles in a 50:50 by weight mixture were implanted in an ovine hemi-arthroplasty model. Post-operative assessments of locomotor function, radiographic appearance and quantitative changes in mineralisation around the graft were made at 2, 4 and 6 months. Post-mortem assessments of radiographic and histologic appearance of the grafts were made at 6 months. No significant differences were noted in any of the measured or assessed parameters between the two graft types. The glass ionomer particles seemed to be well tolerated within the matrix of new bone, smaller sized particles appearing to be better incorporated than larger ones. The use of particles of glass ionomer as a bone graft expander, in this in vivo model of revision hip arthroplasty, would therefore appear to offer no detriment in performance over pure allograft in the short to medium term.

Fibronectin is an extracellular matrix glycoprotein involved in wound healing. Techniques have been developed for the preparation of orientated fibronectin mats from plasma fibronectin, for use in wound healing and tissue repair. Formation of strands and mats is by self-association and aggregation of fibronectin from solution under a directional shear force. Incorporation of heparin with fibronectin modified the mats. Scanning electron microscopy showed that the mats were composed of well-orientated fibrous fibronectin, with a network of internal interconnecting pores. Single strands of fibronectin were prepared for use as a tissue culture model of cell interaction with aggregated orientated fibronectin mats. Rat tail tendon and human skin fibroblasts were used for assessment of cell interaction with both single strands of fibronectin and mats. Fibroblasts rapidly attached to single strands and became orientated. Dense cultures of fibroblasts growing over single strands became orientated, according to the orientation of the underlying fibronectin. Fibroblasts readily grew on the surface of fibronectin mats and were observed within the porous network.

The purpose of this investigation was to determine which geometric and surface properties encouraged optimal ingrowth and bonding of bone to an extra-cortical plate. Forty-eight titanium extra-cortical plates were attached onto the left and right femora of adult rabbits. The plates were of six different designs and the osseoconductive effects of four surfaces were examined. A roughened titanium surface, a plasma sprayed HA coating of low crystallinity (57%) and a solution precipitated calcium phosphate coating were compared with a plasma sprayed crystalline hydroxyapatite coating (crystallinity 85%). Thin sections were prepared by grinding and polishing. Bone formation and the interface around the plates were investigated histologically and computer and morphometric analyses were used to quantify new bone formation, bone apposition onto the plate, bone porosity and the condition of the HA coating. The study found that a hydroxyapatite coating (with the exception of the solution precipitated coating) had significantly greater interfacial contact with bone when compared to a roughened titanium surface, and that significantly more bone attached to a crystalline HA coating compared with the HA coating of lower crystallinity although significantly more bone formed in the vicinity of the lower crystalline HA coating. Differences in the bony reaction induced by the various geometric designs were evident and the optimal plate design requires either holes or slots along its length as this encouraged bone ingrowth into the plate.

Using a variety of cell types, cell attachment and growth was studied on prospective (polyethersulphone (PES) and polyetheretherketone) and currently used (titanium 318 alloy, cobalt chrome molybdenum alloy and ultra-high molecular weight polyethylene (UHMWPE)) orthopaedic biomaterials. Proliferation of fibroblasts and osteoblasts was measured using incorporation of tritiated thymidine into total DNA. Attachment of cells was assessed by indirect immunofluorescent labelling of vinculin, a component of the cell's focal adhesion plaque. The degree of cell attachment was quantified on the materials by determining the mean number of adhesion plaques and using an image analysis system to determine the mean total area of plaques per cell. Fibroblasts and osteoblasts responded differently to the materials tested. When grown on PES surfaces, rat tail fibroblasts synthesized significantly greater amounts of DNA than cells on all other surfaces, whilst fibroblasts on UHMWPE synthesized significantly less DNA than cells on all other materials. Interestingly, there was no significant difference between the amounts of DNA synthesized by osteoblasts grown on the various materials. Determination of the number of vinculin adhesion plaques per cell and the mean total area of the plaques per cell showed that the attachment of fibroblasts to UHMWPE was significantly reduced compared with other materials. In contrast there was no significant difference in the adhesion of osteoblasts to different materials. Scanning electron microscope (SEM) observations of cells on the materials correlated with the morphometric data. Cells with the greatest number and area of adhesion plaques were well spread and flattened whilst those with the least number of adhesion plaques were more rounded and less spread.

The biochemical characteristics of a novel biomaterial, based on the aggregated adhesive protein, fibronectin (Fn), are reported here. Fibrous, orientated mats, formed from solution under directional shear, could be made to incorporate heparin (typically 3.2 mu mg/mg fibronectin). Mats were hygroscopic, doubling their mass by water uptake in less than 10 h from humid air. After an initial rapid loss of protein into physiological solutions over 24 h, mats were stable and not rapidly degraded by fibroblasts. With or without heparin, mats bound basic fibroblast growth factor, which was then released only slowly. Such materials may prove useful models of in vivo tissue Fn function and as clinical implants to organize tissue repair.